Shafting having flats and method of producing such flats and shafting



C. HERZOG Feb. 21, 1967 3,304,761 FLATS AND METHOD OF PRODUCING sucn FLATS AND SHAFTING SHAFTING HAVING Filed March 13, 1964 INVENTOR.

CARL HERZOG a P yaw.

ATTORNEY United States Patent 3,304,761 SHAFTING HAVING FLATS AND METHOD OF PRODUCING SUCH FLATS AND SHAFTING Carl Herzog, 11 38th Place, Long Beach, Calif. 90806 Filed Mar. 13, 1964, Ser. No. 351,789 4 Claims. (Cl. 72-377) This application is a continuation-in-part of my prior copending application Serial Number 234,700, now abandoned, filed Nov. 1, 1962, for Machine Element Assembly and Method of and Apparatus for Producing Same.

This invention relates to shafting or the like for use in miniature machine element assemblies and to a method of producing such shafting.

More particularly, the invention is concerned with a method of forming flats upon shaft elements or the like with a very high degree of accuracy and uniformity and with economy, whereby the processed shaft elements may be subsequently assembled with small gears or like machine elements in a very secure manner and with almost perfect concentricity. On a production basis, concentricity of the assembly within .00005 inch average indicator reading may be unfailingly obtained, when dealing with shafts of one-eighth inch diameter.

My method of producing flats on shafting or the like is based upon the compressibility of metals which is a known factor but one which has seldom, if ever, been utilized in practice. This compressibility factor or characteristic of metals is distinguished from ductility of metals which is an entirely different characteristic taken advantage of for forging, coining and reshaping of metals, wherein the metal actually flows and is permanently reformed or deformed. In my method, I utilize the inherent compressibility characteristic for producing the permanent minute flats upon shafting or the like with a very high degree of accuracy.

My method involves a concentration of stress upon an initially round metal shaft element within the compressibility range (yield strength) of the metal and setting or deforming the metal locally, without effecting the remainder of the material. It is believed that the locally stressed areas of the shaft element have their molecules permanently rearranged in closer proximity than in adjacent unstressed areas and throughout the remainder of the shaft element. This explains how and why my method effects the formation of the minute flats on shaft elements without changing the physical dimensions of the remainder of the shaft elements.

The elastic limit of a material is the maximum unit stress to which the material may be subjected and still be able to return to its original shape upon removal of the stress. Hookes law applies here, and stress and strain are equal. When a material is stressed a small and controlled amount beyond its elastic limit, then the material after removal of the stress will return only partially to its original form or shape, and thereby acquires a permanent deformation or set. This deformation or set, where the unit stress is held below the yield point of the material, is due to the compressibility of the material and this factor or characteristic is taken advantage of in the present invention. In other words, the invention method causes in the stressed material only a borderline entry into the area of proportional limit and only locally changes the modulus of the material. Resulting deformation or set will appear only in the local areas where the stresses are concentrated. Thus, in an initially round bar of metal, the method will result in a pair of diametrically opposed minute flats without deforming the remainder of the bar. In this method, the stresses to which the material is subjected are never so great that the compressibility factor of the material is exceeded. If the stresses are too great,

Patented Feb. 21, 1967 the yield point of the material will be reached and at this point or beyond it, the shape of the entire material element will be altered and this latter condition must be avoided in the present method.

As will appear hereinafter, means is provided in the.

form of spacer elements to control the stress on the material so that the stress will be above the elastic limit of the material and always below the yield point. The spacer elements are dimensioned to compensate for the elasticity (spring-back) of the material and at the same time make it impossible for the material to reach the yield point.

The invention is concerned mainly with shaft elements formed of corrosion-resistant steels (stainless steel) such as AISI 303 and AISI 416 types. However, other steels including cold rolled and certain alloys are also suitable for the method, provided their hardness range is between approximately 20 C and 48 C Rockwell. This eliminates the very hard and very soft metals which are not suitable for the present method.

My prior Patent 2,804,322, issued Aug. 27, 1957, for Rotary Element and Shaft Assembly, discloses the type of miniature machine element assembly to which the present invention pertains. As shown in this prior patent, a female component such as a miniature gear has its bore provided with circun'iferentially spaced flats by broaching or the like. The male element or shaft is provided with coacting flats formed by grinding or the like and the two elements are then assembled telescopically with the minimum practical clearance between the male and female elements and then rotated relative to each otheruntil lines of contact are established on the coacting flats of the male and female elements. Easy flowing epoxy adhesive or cement is then introduced into the spaces between the interfitting machine elements while the contacting relationship of the flats is maintained and the spaces are entirely filled with the cement. When the cement cures or hardens, the machine elements are locked together in assembled relationship and concentrically and an extremely secure bond is established between the elements in this manner.

The main object of the present invention is to improve upon the accuracy of the assembly disclosed broadly in my prior patent and to provide a more economical, reliable and much more practical and accurate method of forming the flats on the male element or shaft, resulting in a much higher degree of concentricity in the assembly.

My present method of producing flats on shafting eliminates entirely the costly grinding of the miniature shafting and eliminates the heat incident to grinding which results in some warpage of the shafting. The accuracy of the flats and the resulting concentricity of the machine element assemblies cannot be obtained by conventional shaft processing methods such as grinding or external breaching. The flats formed by my method are free of surface markings and no deformation or metal flow is observable even under microscopic examination. My method of producing the flats has the added advantage of tending to straighten the shafting rather than bending or warping it, as sometimes occurs under conventional methods.

The present invention is conjunction with the teachings; of my prior patent and application produces added advantages in the resulting miniature assemblies. The necessity for step shafts is eliminated (unit design is achieved); no set screws need be employed; no selection and lapping of shafts is required; no skilled labor is needed for assembly; no chip contamination is encountered at assembly; no arbor pressing; no drilling for dowel pins and no reaming is required; and there is no warpage of the assembly due to pinning or other mechanical fastening. Smaller shafts can be employed due to the elimination of dowel holes. The miniature assemblies produced are ideally suitable for no back-lash gearing, output shafts of miniature motors, potenti-ometers, etc. These and other advantages will be apparent to those skilled in the art.

Other objects and advantages of the invention will be apparent during the course of the following detailed description.

In the accompanying drawings forming a part of this application and in which like numerals are employed to designate like parts throughout the same,

FIGURE 1 is a perspective view on a greatly enlarged scale of a shaft element having flats formed thereon in accordance with my method,

FIGURE 2 is a greatly enlarged fragmentary cross section through the shaft embodying the invention and showing one of the minute flats formed by compressing the metal without causing metal flow or deformation,

FIGURE 3 is a similar view showing the undesirable result which would be obtained were the shaft compressed so much that metal displacement or flow or deformation resulted, and

FIGURES 4 to 7 inclusive are partly diagrammatic views of forming die means employed to produce flats on the shafting by utilizing the compressibility of the metal from which the shafting is made.

In the drawings, wherein for the purpose of illustration is shown a preferred embodiment of the invention, attention is directed first to FIGURES 4 to 7 inclusive illustrating the apparatus components used in the practice of the method. In these figures, a lower forming die 10 is provided formed of hard material and having a substantially perfectly flat top face 11. The die 10 is secured to the table, not shown, of a hydraulic press having a ram 12. The ram 12 carries an upper movable die 13 having a flat bottom face 14 which is strictly parallel to the face 11 of the lower die 10. Accurately formed spacer blocks 15 are secured to the lower forming die 10 in spaced parallel relation to provide between them a space 16 for the shaft 17 being processed. The shaft 17 is initially cylindrical as shown in FIGURE 4 on a very exaggerated scale. The top faces 18 of spacer blocks 15 are flat and are arranged in exactly the same elevation above the lower die 10 and are parallel to the opposed flat faces 11 and 14 of the dies.

With the shaft 17, such as a one-eighth inch diameter shaft, positioned in contact with the die faces 11 and 14, FIGURE 4, but under no compression from the dies, the space 19 between the upper die face 14 and the spacer block faces 18 is equal approximately to twice the depth of each diametrically opposed flat which is to be formed upon the shaft 17 by compression. For a one-eighth inch diameter shaft, the diametrically opposed pair of parallel flats which will be formed as shown in FIGURE 5 will each be approximately .0005 inch deep measured from the periphery of the shaft. As previously explained, the degree of compression of the shaft to allow formation of these shallow yet perfectly defined identical flats is not sufficient to cause deformation or flowof the metal of the shaft to produce a forging effect as depicted in FIGURE 3. However, the compression of the shaft is suflicient to permanently compress the metal and provide thereon a pair of identical flats 20 when the upper die 13 is lowered into contact with the spacer blocks 15 as depicted in FIGURE 5. The diametrically opposed flats 20 which are truly parallel and equal in depth are also permanent in nature in the sense that the compression of the metal is of suflicient degree so that there can be no elastic recovery to the original cylindrical shape of the shaft 17. Neither is there any metal flow or displacement of metal to cause the undesirable result shown in FIGURE 3. As explained in the introductory portion of the specification, during the above-described formation of the flats 20, the stress on the shaft element 17 is controlled accurately so as to be above the elastic limit of the metal but always below the yield point thereof. .This controlled stress prevents the shaft element from recovering to its initially cylindrical shape and also prevents it from having its original shape changed except at the local areas of stressing or at the flats 20.

As shown in FIGURES 4 and 5, the upper die 13 is closed into positive engagement with the top faces 18 of spacer block 15 and the identical flats 20 are immediately formed on the shaft element, with each flat being of a depth equal to one-half of the width of the space 19 present in FIGURE 4 when the upper die is in tangential contact with the shaft 17 without compression. The flats 20 are smooth surfaced and free of markings, burrs or the like. There will be no contamination caused by metal chips or shavings because there is no machining or grinding during the invention process.

FIGURE 2 shows one of the flats 20 formed on the shaft by the invention process on a greatly exaggerated scale and indicating that there is none of the metal flow or displacement illustrated in FIGURE 3, showing the undesirable condition which would be obtained if the metal were compressed beyond the limit of its inherent compressibility or beyond the yield point thereof.

As should now be apparent, the prime purpose of the spacer blocks 15 is to control the stressing of the shaft element 17 so that the stress is above the elastic limit of the metal but below the yield point. The spacer blocks are accurately dimensioned to compensate for the elasticity (spring-back) of the shaft material, while at the same time, making it impossible for the shaft material to be stressed to the yield point. I have found that the trial and error method of dimensioning the spacer blocks 15 is the most satisfactory. Calculating the dimensions of the spacer blocks is not practical because too many variables are involved. For example, the spacer blocks 15 themselves are subject to elasticity or spring-back. However, once the proper dimensioning of the spacer blocks is found by trial and error, the invention apparatus and process gives unfailingly good and uniform results.

FIGURES 6 and 7 illustrate the manner in which additional identical pairs of diametrically opposed flats 20 may be formed upon the shaft 17 by the same invention process after proper and accurate indexing of the shaft by any suitable means, not shown. Suitable indexing means for this purpose is disclosed in my mentioned prior application Serial Number 234,700, but it is desired not to limit the present method to any particular means for indexing and such means may be conventional.

FIGURE 6 shows the formation of a second identical pair of flats 20 on the shaft 17 spaced circumferentially from the first pair of flats 20. The operation of the die means in FIGURE 6 is identical to the operation shown in FIGURES 4 and 5 and is merely repetitive after indexing.

FIGURE 7 illustrates the operation of the die means for forming a third diametrically opposed identical pair of minute flats 20 on the shaft 17 after further indexing. As shown in FIGURE 7, the completed shaft 17 is now provided with six identical circumferentially equidistantly spaced flats 20 by the novel compression process.

The die structure is made long enough axially of the shaft to process or compress the entire length of the shaft whatever that length may be in practice. The processing of the flats on the shaft tends to maintain the shaft straight and actually improves the straightness thereof.

FIGURE 1 shows the completely processed shaft 17 after the several flats 20 have been formed thereon in the manner described and illustrated in connection with FIG- URES 4 to 7. The completed shaft is then utilized in the making of miniature machine element assemblies generally in the manner disclosed in my mentioned prior patent and more specifically in the manner disclosed in my mentioned application. However, the present invention which is basic to the formation of these miniature assemblies is concerned solely and primarily with the shaft per se having flats and the method of forming the flats utilizing the compressibility factor of metals. The advantages of the.

invention should now be readily apparent to those skilled in the art without the need for any further description.

It is to be understood that the form of my invention herewith shown and described is to be taken as a preferred example of the same, and that various changes in the shape, size and arrangement of parts may be resorted to, without departing from the spirit of the invention or scope of the subjoined claims.

Having thus described my invention, I claim:

1. A method of producing highly accurate and uniform minute flat surfaces by compression alone on an initially cylindrical shaft which is formed of metal having a hardness range of approximately 20 C to 48 C Rockwell, said method comprising arranging the cylindrical shaft between a pair of opposed parallel flat-faced pressure-applying elements, moving said elements relatively toward each other and thereby compressing the shaft diametrically between the flat-faced elements so that the metal of the shaft in the local regions thereof engaged by the flat-faced elements is stressed slightly beyond the elastic limit of the metal but well below its yield point, the remainder of the shaft then being subjected to modest stressing only well below the elastic limit of the metal, positively limiting said relative movement of the flat-faced elements toward each other so that the stress in said local regions will not greatly exceed said elastic limit and so that the degree of stress may be controlled with high accuracy, and then releasing said shaft, the released shaft having permanent minute fi-at surfaces thereon at diametrically opposite sides thereof and the remainder of the shaft retaining its original cylindrical shape and being undeformed.

2. A method of producing highly accurate and uniform minute fiat surfaces by compression alone on an initially cylindrical shaft which is formed of metal having a hardness range of approximately 20 C to 48 C Rockwell as defined in claim 1, and wherein said flat-faced pressureapplying elements engage said shaft throughout its entire length so that said flat surfaces extend continuously for the full length of the shaft.

3. A method of producing highly accurate and uniform minute fiat surfaces by compression alone on an initially cylindrical shaft which is formed of metal having a hardness range of approximately 20 C to 48 C Rockwell as defined in claim 1, and then indexing the shaft on its longi tudinal axis a desired number of times and repeating the method after each indexing to form on the shaft any desired number of additional diametrically opposed flat surfaces substantially identical to the first produced fiat surfaces.

4. A method of producing highly accurate and uniform minute flat surfaces on a miniature initially cylindrical metal shaft solely by compressing the shaft, the shaft formed of metal having a hardness range of approximately 20 C to 48 C Rockwell, said method comprising positioning the shaft between an opposed pair of rigid flatfaced pressure-applying elements, moving the elements relatively toward each other and compressing the shaft diametrically between the elements, positively and accurately limiting the extent of relative movement of the fiat-faced elements toward each other to thereby accurately control the degree of stress in the local regions of the shaft near said elements, and then releasing said shaft.

References Cited by the Examiner UNITED STATES PATENTS 1,907,897 5/1933 Swegles 641 2,067,282 1/1937 Padgett 641 3,220,239 11/1965 Olsen et al. 72404 CHARLES W. LANHAM, Primary Examiner. L. A. LARSON, Examiner. 

1. A METHOD OF PRODUCING HIGHLY ACCURATE AND UNIFORM MINUTE FLAT SURFACES BY COMPRESSION ALONE ON AN INITIALLY CYLINDRICAL SHAFT WHICH IS FORMED OF METAL HAVING A HARDNESS RANGE OF APPROXIMATELY 20 C TO 48 C ROCKWELL, SAID METHOD COMPRISING ARRANGING THE CYLINDRICAL SHAFT BETWEEN A PAIR OF OPPOSED PARALLEL FLAT-FACED PRESSURE-APPLYING ELEMENTS, MOVING SAID ELEMENTS RELATIVELY TOWARD EACH OTHER AND THEREBY COMPRESSING THE SHAFT DIAMETRICALLY BETWEEN THE FLAT-FACED ELEMENTS SO THAT THE METAL OF THE SHAFT IN THE LOCAL REGIONS THEREOF ENGAGED BY THE FLAT-FACED ELEMENTS IS STRESSED SLIGHTLY BEYOND THE ELASTIC LIMIT OF THE METAL BUT WELL BELOW ITS YIELD POINT, THE REMAINDER OF THE SHAFT THEN BEING SUBJECT TO MODEST STRESSING ONLY WELL BELOW THE ELASTIC LIMIT OF THE METAL, POSITIVELY LIMITING SAID RELATIVE MOVEMENT OF THE FLAT-FACED ELEMENTS TOWARD EACH OTHER SO THAT THE STRESS IN SAID LOCAL REGIONS WILL NOT GREATLY EXCEED SAID ELASTIC LIMIT AND SO THAT THE DEGREE OF STRESS MAY BE CONTROLLED WITH HIGH ACCURACY, AND THEN RELEASING SAID SHAFT, THE RELEASED SHAFT HAVING PERMANENT MINUTE FLAT SURFACES THEREON AT DIAMETRICALLY OPPOSITE SIDES THEREOF AND THE REMAINDER OF THE SHAFT RETAINING ITS ORIGINAL CYLINDRICAL SHAPE AND BEING UNDEFORMED. 